After a lot of research here and elsewhere, and after reading Rod Gervais's book, I have hired a builder to make a timber construction - on a concrete slab - in my garden. On top of the slab will be brick to damp level only and the outer timber frame will sit on top of these.

It'll be one room which I want to use for both recording guitars, vocals and drums and also mixing. And I'll be doing the acoustic treatment after build.

The internal dimensions will be L 5.5m, W 3m, H 2.3m. Not perfect on the Amroc calculator, but not too bad either. I am restricted to the above width and digging down further will be a problem.

The floor will be a new concrete slab, with damp proof membrane, then underlay and vinyl sheeting.

The inner wooden wall timber frame will be fixed to the slab on top of acoustic matting.

There will be two fire doors doubled up but no window (although the framing will be such that if I want to add one later this will be possible).

Re HVAC - no air con (maybe next year) but I will have in and out ventilation with ducting above the inner room ceiling that will come through this ceiling at the edge of the room into wall mounted silencer boxes).

What do you think? I am in a quiet area so external noise coming in will not be a significant problem. The nearest house is 20m away (mine is 10m away). I am looking for a db reduction of 50db.

I have a few particular questions below, but would appreciate all comments:

Does the above give me a true two-leaf set up?
Is using Rockwool RW3 insulation at both points above a good idea?
Do I have enough mass in the outer wall and ceiling?
Should I do anything more to guard against damp?

Andre has a formula for calculating wall resonance, but i couldnt find it. The above pdf should help. The weak point will be your outer leaf. You might need to add more mass, especially to the roof, to hit 50db reduction at LF. Hopefully someone more knowledgeable than myself can chime in though. Good luck, and congratulations!

Based on what I've read here and elsewhere, I've changed my plan and I'm going to have concrete block exterior walls now instead of a timber outer.

The interior decoupled room within a room will be a timber frame with double layer acoustic board as before (walls and ceiling).

I've also asked my builder to dig down 300mm to give me more interior height.

I've properly looked at the planning and building regs and understand what I can do.

I'd appreciate help on the the exterior roof. My budget definitely won't stretch to a concrete roof.
Should I tile it and have acoustic board above the rafters (or will OSB suffice). Then there'll be my gap - within insulation - before the inner ceiling of double acoustic board as above. Will this be sufficient mass? How can I beef it up if needed?

Also, on the exterior block walls, my builder is talking about putting batons on the outside of the block, and putting timber cladding on them. Will the gap between the block and the cladding matter? Should I insulate that?

Good idea. Like Andre said, just use regular fire rated gypsum. Whats your plan for the roof? Is it going to be a standard truss roof with ventilated soffits? Or sealed to the brick outer leaf?

It's going to be an apex roof with a void above the inner room ceiling. I'm currently trying to work out what I need to do - within my budget - to beef up the mass of the outer roof. It was originally to be OSB sheets with felt shingle roof tiles but, now I'm having block walls, I need to do more.

A cement roof isn't doable for me. Should I double up on the OSB? Use a layer of cement bonded particle board? Or use one or two layers of fire board under the OSB, between the rafters?

It's going to be an apex roof with a void above the inner room ceiling. I'm currently trying to work out what I need to do - within my budget - to beef up the mass of the outer roof. It was originally to be OSB sheets with felt shingle roof tiles but, now I'm having block walls, I need to do more.

A cement roof isn't doable for me. Should I double up on the OSB? Use a layer of cement bonded particle board? Or use one or two layers of fire board under the OSB, between the rafters?

Cheers

First you have to know the sound reduction the wall realizes.
How thick is the concrete wall?
Yoy have a 100 mm wool filled gap and then the OSB?

It's going to be an apex roof with a void above the inner room ceiling. I'm currently trying to work out what I need to do - within my budget - to beef up the mass of the outer roof. It was originally to be OSB sheets with felt shingle roof tiles but, now I'm having block walls, I need to do more.

A cement roof isn't doable for me. Should I double up on the OSB? Use a layer of cement bonded particle board? Or use one or two layers of fire board under the OSB, between the rafters?

Cheers

Maybe I missed it but how is the concrete block wall constructed and exactly how you are going to build the timber wall? 100 mm woolfilled gap with OSB?
If that is clear you can determine the sound reductuion of the wall and see what you need on the roof.

Are you the same John who messaged me on JLSayers? I'm waka over there (sorry I realised I didn't reply)

Remember that you don't need the same mass on your roof outer leaf as on your walls. You need a similar TL. You can achieve this in a number of ways. Why not increase the sealed cavity depth in your roof?

Also remember that in the UK, if you have an unventilated roof you have to thermally insulate above the roof deck, (warm roof design). If you are building cold roof then you need it ventilatated along the entire length of the long wall soffits for flat roofs.
To achieve any good TL with a ventilated roof you have to go 3 leaf and board underneath the roof joists with extra substantial mass, seal this layer and build your inner leaf below this.

Are you the same John who messaged me on JLSayers? I'm waka over there (sorry I realised I didn't reply)

Remember that you don't need the same mass on your roof outer leaf as on your walls. You need a similar TL. You can achieve this in a number of ways. Why not increase the sealed cavity depth in your roof?

Also remember that in the UK, if you have an unventilated roof you have to thermally insulate above the roof deck, (warm roof design). If you are building cold roof then you need it ventilatated along the entire length of the long wall soffits for flat roofs.
To achieve any good TL with a ventilated roof you have to go 3 leaf and board underneath the roof joists with extra substantial mass, seal this layer and build your inner leaf below this.

Are you the same John who messaged me on JLSayers? I'm waka over there (sorry I realised I didn't reply)

Remember that you don't need the same mass on your roof outer leaf as on your walls. You need a similar TL. You can achieve this in a number of ways. Why not increase the sealed cavity depth in your roof?

Also remember that in the UK, if you have an unventilated roof you have to thermally insulate above the roof deck, (warm roof design). If you are building cold roof then you need it ventilatated along the entire length of the long wall soffits for flat roofs.
To achieve any good TL with a ventilated roof you have to go 3 leaf and board underneath the roof joists with extra substantial mass, seal this layer and build your inner leaf below this.

Dan

Hi Dan

I spoke to my builder. The plan is for a warm roof. On top of the roof joists it'll comprise plastic tapco tiles on top of membrane then kingspan slab insulation sitting on two layers of 22mm OSB with green glue between. Then between the joists I was going to put a layer of fire board.

Below that will be my room within a room, which will be made of RW3 insulation (100mm) then two layers of fireboard with green glue between.

I imagine the roof cavity from inner ceiling to apex will be between 0.5m-1m (I can check this) and I was going to stuff this with soft insulation also. (It's also where the ventilation for the inner room ducting will be).

Maybe I missed it but how is the concrete block wall constructed and exactly how you are going to build the timber wall? 100 mm woolfilled gap with OSB?
If that is clear you can determine the sound reductuion of the wall and see what you need on the roof.

Hi Bert

The outer walls are made of 100mm concrete breeze block. These are built on concrete footings which are set deeper than the concrete slab of the inner room. There will be a 75mm cavity (unfilled) then a 100mm layer of Rockwool RW3 insulation. My inner wall with comprise an OSB sheet then two layers of fire board with green glue between.

I have decided to paint the exterior in masonry paint rather than have wooden cladding due to both cost and also to avoid possible resonance issues.

I spoke to my builder. The plan is for a warm roof. On top of the roof joists it'll comprise plastic tapco tiles on top of membrane then kingspan slab insulation sitting on two layers of 22mm OSB with green glue between. Then between the joists I was going to put a layer of fire board.

Below that will be my room within a room, which will be made of RW3 insulation (100mm) then two layers of fireboard with green glue between.

I imagine the roof cavity from inner ceiling to apex will be between 0.5m-1m (I can check this) and I was going to stuff this with soft insulation also. (It's also where the ventilation for the inner room ducting will be).

Does this sound reasonable to you?

Thanks

John

Hi John warm roof design sounds good. A couple of notes:

I spoke to green glue and they say it doesnt work as well between osb as its specifically designed for between 2 plasterboard layers.

How much TL you need? You might be overkilling the roof. 2x22mm osb3 and a layer of fibreboard is pretty good on its own for an outer leaf without the green glue. Green glue between 2 plasterboard gives a similar TL to 3 layers of plasterboard without greenglue.

If I were you, as long as you dont have height constraints, I wouldnt put green glue on the outer leaf at all. I would go with 2 x osb3 on their own, and inner leaf use 2 x fireboard with green glue and increase the cavity depth until the roof has a resonant frequency half the frequency you want to isolate (completely filling the cavity with low density insulation). Cavity depth is the cheapest way to improve TL (unless you're building yourself, where adding another plasterboard layer may be cheaper then the extra insulation)

Your inner leaf ceiling doesn't need RW3 in. Studies show that low density insulation performs better at low frequencies in a MAM assembly. Replace the 100mm of RW3 with a lower density loft roll and completely fill the roof void ceiling to roof deck. This will perform better and be cheaper (loft roll is ridiculously cheap). Your insulation shouldn't really be used for increasing mass. Increase mass with boarding materials, this is much more effective.

The outer walls are made of 100mm concrete breeze block. These are built on concrete footings which are set deeper than the concrete slab of the inner room. There will be a 75mm cavity (unfilled) then a 100mm layer of Rockwool RW3 insulation. My inner wall with comprise an OSB sheet then two layers of fire board with green glue between.

I have decided to paint the exterior in masonry paint rather than have wooden cladding due to both cost and also to avoid possible resonance issues.

Cheers

John

As with the roof design I would forget the RW3 in the walls. Fill the entire 175mm with a lower density self supporting wall insulation (this is likely alot cheaper too). Your block wall has plenty of mass, you just need to absorb resonance, and lower the resonant frequency.

The blocks probably wont resonate much at all you know? Cladding wouldnt cause you any problems. You should paint the concrete anyway though to seal it. Then face it with whatever you like the look of.

As with the roof design I would forget the RW3 in the walls. Fill the entire 175mm with a lower density self supporting wall insulation (this is likely alot cheaper too). Your block wall has plenty of mass, you just need to absorb resonance, and lower the resonant frequency.

The blocks probably wont resonate much at all you know? Cladding wouldnt cause you any problems. You should paint the concrete anyway though to seal it. Then face it with whatever you like the look of.

Cheers Dan. I've ordered the RW3 after reading several people used it in their studio. I can't change that. Will it still offer me resonance absorption?

The outer walls are made of 100mm concrete breeze block. These are built on concrete footings which are set deeper than the concrete slab of the inner room. There will be a 75mm cavity (unfilled) then a 100mm layer of Rockwool RW3 insulation. My inner wall with comprise an OSB sheet then two layers of fire board with green glue between.

I'm not the OP but I've run his wall design through a spreadsheet used at JLSayers and this wall design has the potential for a Transmission Loss of 70dB down to 40Hz.

I'm not sure on John's requirements but this is very high, and may not be necessary (especially considering the roof and especially the doorway will be VERY expensive and difficult to get near this.)

John, if you cant afford 65-70dB TL on your doors and roof then save money on your walls, drop the green glue and reduce to just a single layer of OSB and 1 layer of fireboard. This can still push 60dB.

I'm not the OP but I've run his wall design through a spreadsheet used at JLSayers and this wall design has the potential for a Transmission Loss of 70dB down to 40Hz.

I'm not sure on John's requirements but this is very high, and may not be necessary (especially considering the roof and especially the doorway will be VERY expensive and difficult to get near this.)

John, if you cant afford 65-70dB TL on your doors and roof then save money on your walls, drop the green glue and reduce to just a single layer of OSB and 1 layer of fireboard. This can still push 60dB.

Dan

Thanks Dan. I really appreciate your advice.

I was aiming for 50-60dB TL so good news on the walls.

For the door I'm having an inner solid fire door decoupled from an outer solid composite door.